<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body {
      height: 100vh;
      background-color: black;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .box {
      width: 200px;
      height: 100px;
      background: white;
      margin: 20px;
    }

    .box:nth-child(1) {
      /* 0deg为从下垂直向上 */
      background: 
        linear-gradient(135deg, transparent 10px, white 0) left top ,
        linear-gradient(45deg, transparent 10px, white 0) left bottom,
        linear-gradient(-45deg, transparent 10px, white 0) right bottom,
        linear-gradient(-135deg, transparent 10px, white 0) right top;
      background-size: 51% 51%;
      background-repeat: no-repeat;
    }
    .box:nth-child(2) {
      /* 0deg为从下垂直向上 */
      background: 
        radial-gradient(circle at 0 0, transparent 20px, white 0) left top,
        radial-gradient(circle at 0 100%, transparent 20px, white 0) left bottom,
        radial-gradient(circle at 100% 100%, transparent 20px, white 0) right bottom,
        radial-gradient(circle at 100% 0, transparent 20px, white 0) right top;
      background-size: 51% 51%;
      background-repeat: no-repeat;
    }

    .box:nth-child(3) {
      clip-path: polygon(
        14.4px 0, 
        calc(100% - 14.4px) 0,
        100% 14.4px,
        100% calc(100% - 14.4px),
        calc(100% - 14.4px) 100%,
        14.4px 100%,
        0 calc(100% - 14.4px),
        0 14.4px
      );
      transition: .5s clip-path
    }

    .box:nth-child(3):hover {
      clip-path: polygon(
        0 0,
        0 0,
        100% 0,
        100% 0,
        100% 100%,
        100% 100%,
        0 100%,
        0 100%
      );
      /* background: red; */
    }
  </style>
</head>
<body>
  <div class="box">

  </div>
  <div class="box">

  </div>
  <div class="box">
    这里要注意，clip-path的过渡，要保证点数一样
  </div>
  <div class="box">

  </div>
</body>
</html>